1. Field of the Invention
This invention relates to a process for producing .alpha.-olefin polymers by the use of a novel catalyst which is suitable for .alpha.-olefin polymerization, particularly gas phase polymerization, and further, as a modification of gas phase polymerization, a combination of slurry or bulk polymerization with gas phase polymerization.
2. Description of the Prior Art
It is well known that .alpha.-olefins are polymerized by the use of so-called Ziegler-Natta catalysts comprising a compound of transition metals of IV-VI Groups of the Periodic Table and an organometallic compound of metals of I-III Groups of the Table, including modified catalysts obtained by further adding an electron donor, etc. thereto. Among the catalysts, those comprising titanium trichloride as the component of transition metal compound have been most widely employed for obtaining highly crystalline polymers of e.g. propylene, butene-1, etc. Such titanium trichloride is classified into the following three kinds according to its preparation:
(1) A material obtained by reducing TiCl.sub.4 with hydrogen, followed by milling with ball mill for activation, which material has been referred to as titanium trichloride (HA).
(2) A material obtained by reducing TiCl.sub.4 with metallic aluminum, followed by milling with ball mill for activation, which material is expressed by the general formula TiCl.sub.3 .multidot.1/3AlCl.sub.3 and has been referred to as titanium trichloride (AA).
(3) A material obtained by reducing TiCl.sub.4 with an organoaluminum compound, followed by heat treatment.
However, since any of these titanium trichlorides have not been satisfactory enough, various improvements have been attempted and proposed. Among them, a process has been proposed wherein a titanium trichloride obtained by reducing TiCl.sub.4 with an organoaluminum compound is treated with an electron donor and TiCl.sub.4 whereby the catalyst activity is enhanced and the amount of amorphous polymer byproduced is reduced (e.g. Japanese patent application laid-open No. 34478/1972). However, the catalysts obtained according to these processes have a drawback that they are deficient in the heat stability.
Further, a process has been proposed wherein TiCl.sub.4 and an organoaluminum compound are separately mixed with a definite amount of a complex-forming agent (electron donors being a kind thereof), to obtain two mixture liquids which are then mixed together and reacted to prepare a solid catalyst component (Japanese patent application laid-open No. 9296/1978). However, this process, too, has a drawback that the catalyst is deficient in the heat stability, as in the case of the above Japanese patent application laid-open No. 34478/1972.
Still further, a process wherein a uniform liquid material consisting of an organoaluminum compound and an ether is added to TiCl.sub.4 or TiCl.sub.4 is added to the former liquid to prepare a liquid material containing titanium trichloride (Japanese patent application laid-open No. 115797/1977), as well as a process wherein the above-mentioned liquid material is heated to a temperature of 150.degree. C. or lower to precipitate a finely particulate titanium trichloride (Japanese patent application laid-open No. 47594/1977, etc.) have been proposed.
However, these processes, too, have a drawback that the catalysts are deficient in the heat stability.
On the other hand, as for processes for polymerizing .alpha.-olefins wherein Zeigler-Natta catalysts are employed but the phase of .alpha.-olefins is varied, slurry polymerization carried out in a solvent such as n-hexane, etc. (e.g. Japanese patent publication No. 10596/1957), bulk polymerization carried out in a liquefied .alpha.-olefin monomer such as liquefied propylene (e.g. Japanese patent publication Nos. 6686/1961, 14041/1963), and gas phase polymerization carried out in a gaseous monomer such as gaseous propylene (e.g. Japanese patent publication Nos. 14812/1964, 17487/1967, etc.), have been well known. Further, a process of bulk polymerization followed by gas phase polymerization has been also known (e.g. Japanese patent publication No. 14862/1974, Japanese patent application laid-open No. 135987/1976, etc.). Among these polymerization processes, gas phase one is advantageous in that recovery and reuse of solvent employed in polymerization as in the case of slurry polymerization process are unnecessary; recovery and reuse of liquefied monomer such as liquefied propylene as in the case of bulk polymerization process are unnecessary; hence the cost of solvent or monomer recovery is small to simplify the equipments for producing .alpha.-olefin polymers; etc. These gas phase polymerization processes, however, have had such disadvantages that since the monomer inside the polymerization vessel is present in vapor phase, the monomer concentration is relatively low as compared with those in slurry or bulk polymerization process, resulting in a lower reaction rate; thus, in order to increase the polymer yield per unit weight of catalyst, it has been necessary to extend the retention time and hence make the capacity of the reactor larger, and also, in order to enhance the catalyst activity, trialkylaluminums have been modified and used, resulting in reduction of the stereoregularity of polymer. In the case of gas phase polymerization process, however, uneven catalyst particles are liable to result in uneven polymer particles. This is, in turn, liable to cause cohesion of polymer particles and clogging of polymer-discharging port of polymerization vessel or transportation line, to make difficult its long time, stabilized, continuous operation and also make the quality dispersion of polymers larger.
The present inventors have previously invented a polymerization process free of the above-mentioned drawbacks even in the case of gas phase polymerization, that is, a process for producing .alpha.-olefin polymers using a catalyst prepared by reacting a reaction product of an electron donor with an organoaluminum compound, with TiCl.sub.4, in the presence of an aromatic compound to form a solid product, or reacting this solid product further with an electron donor to form a solid product; and combining the solid product thus obtained, with an organoaluminum compound.
The inventors have further made studies, and as a result, have invented a process comprising reacting an organoaluminum compound with an electron donor to obtain a reaction product; reacting this reaction product with TiCl.sub.4 to obtain a solid product; reacting this solid product with an electron donor and an electron acceptor to obtain another solid product; combining this solid product with an organoaluminum compound to obtain a catalyst; and polymerizing an .alpha.-olefin in the presence of this catalyst (this process will be hereinafter referred to as prior invention). According to this polymerization process, particularly in the case of gas phase polymerization in the presence of a catalyst obtained by subjecting the catalyst of the above-mentioned process to a preliminary activation with an .alpha.-olefin, a long time stabilized operation without forming any polymer lump has become possible even in the case of gas phase polymerization, but the polymer yield per g of the solid catalyst component was 5,000 to 6,000 g, i.e. the activity of the catalyst could not have been regarded as sufficient. Thus, the amount of catalyst employed could not have been reduced. If the amounts of alcohol, alkylene oxide, steam, etc. employed for killing of catalyst after production of .alpha.-olefin polymers or for purification of polymer are reduced too much, then corrosive substances remaining in polymer have often been not made unharmless, resulting in rusting of mold at the time of molding of polymer or harming the physical properties of polymer.
The present inventors further continued studies for improvement, and as a result have found that if an unknown catalyst component is combined with the catalyst employed in the prior invention, and in this combination, the resulting catalyst components are subjected to polymerization treatment with an .alpha.-olefin and employed for polymerization, then, even in the case of gas phase polymerization, no polymer lump is not only formed, but also the polymer yield can be sufficiently increased and polymer purification can be easily be carried out; it is possible to produce polymer, particularly polypropylene, under control of its stereoregularity; and the rate of atactic polymer formed is low, and have attained the present invention.